src/ir/table-utils.cpp

/*
 * Copyright 2021 WebAssembly Community Group participants
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include "table-utils.h"
#include "element-utils.h"
#include "find_all.h"
#include "module-utils.h"

namespace wasm::TableUtils {

std::set<Name> getFunctionsNeedingElemDeclare(Module& wasm) {
  // Without reference types there are no ref.funcs or elem declare.
  if (!wasm.features.hasReferenceTypes()) {
    return {};
  }

  // Find all the names in the tables.

  std::unordered_set<Name> tableNames;
  ElementUtils::iterAllElementFunctionNames(
    &wasm, [&](Name name) { tableNames.insert(name); });

  // Find all the names in ref.funcs.
  using Names = std::unordered_set<Name>;

  ModuleUtils::ParallelFunctionAnalysis<Names> analysis(
    wasm, [&](Function* func, Names& names) {
      if (func->imported()) {
        return;
      }
      for (auto* refFunc : FindAll<RefFunc>(func->body).list) {
        names.insert(refFunc->func);
      }
    });

  // Find the names that need to be declared.

  std::set<Name> ret;

  for (auto& kv : analysis.map) {
    auto& names = kv.second;
    for (auto name : names) {
      if (!tableNames.count(name)) {
        ret.insert(name);
      }
    }
  }

  return ret;
}

bool usesExpressions(ElementSegment* curr, Module* module) {
  // Binaryen IR always has ref.funcs for functions in tables for uniformity,
  // so that by itself does not indicate if expressions should be used when
  // emitting the table or not. But definitely anything that is not a ref.func
  // implies we are post-MVP and must use expressions.
  bool allElementsRefFunc =
    std::all_of(curr->data.begin(), curr->data.end(), [](Expression* entry) {
      return entry->is<RefFunc>();
    });

  // If the segment has a specialized (non-MVP) type, then it must use the
  // post-MVP form of using expressions.
  bool hasSpecializedType = curr->type != Type(HeapType::func, Nullable);

  return !allElementsRefFunc || hasSpecializedType;
}

TableInfoMap computeTableInfo(Module& wasm, bool initialContentsImmutable) {
  // Set up the initial info.
  TableInfoMap tables;
  if (wasm.tables.empty()) {
    return tables;
  }
  for (auto& table : wasm.tables) {
    tables[table->name].initialContentsImmutable = initialContentsImmutable;
    tables[table->name].flatTable =
      std::make_unique<TableUtils::FlatTable>(wasm, *table);
  }

  // Next, look at the imports and exports.

  for (auto& table : wasm.tables) {
    if (table->imported()) {
      tables[table->name].mayBeModified = true;
    }
  }

  for (auto& ex : wasm.exports) {
    if (ex->kind == ExternalKind::Table) {
      tables[*ex->getInternalName()].mayBeModified = true;
    }
  }

  // Find which tables have sets, by scanning for instructions. Only do so if we
  // might learn anything new.
  auto hasUnmodifiableTable = false;
  for (auto& [_, info] : tables) {
    if (!info.mayBeModified) {
      hasUnmodifiableTable = true;
      break;
    }
  }
  if (!hasUnmodifiableTable) {
    return tables;
  }

  using TablesWithSet = std::unordered_set<Name>;

  ModuleUtils::ParallelFunctionAnalysis<TablesWithSet> analysis(
    wasm, [&](Function* func, TablesWithSet& tablesWithSet) {
      if (func->imported()) {
        return;
      }

      struct Finder : public PostWalker<Finder> {
        TablesWithSet& tablesWithSet;

        Finder(TablesWithSet& tablesWithSet) : tablesWithSet(tablesWithSet) {}

        void visitTableSet(TableSet* curr) {
          tablesWithSet.insert(curr->table);
        }
        void visitTableFill(TableFill* curr) {
          tablesWithSet.insert(curr->table);
        }
        void visitTableCopy(TableCopy* curr) {
          tablesWithSet.insert(curr->destTable);
        }
        void visitTableInit(TableInit* curr) {
          tablesWithSet.insert(curr->table);
        }
      };

      Finder(tablesWithSet).walkFunction(func);
    });

  for (auto& [_, names] : analysis.map) {
    for (auto name : names) {
      tables[name].mayBeModified = true;
    }
  }

  return tables;
}

} // namespace wasm::TableUtils